Percussive tool



F. ABT

PERCUSSIVE TOOL Nov. 24, 1953 2 Sheets-Sheet l Filed oct. 25, 195ol l lw,

ig M l/l/lIlI/ll ATTOR N EY F. ABT

PERcUssIvE Toor.

2 Sheets-Sheet 2 Filed OCT.. 25, 1950 Eng EL INVENTOR Ill/IIIIIIIIIII/II Franz Abt 77 ATTORNEY Patented Nov. 24, 1953 PERCUS SIV ETOOL Franz Abt, Essen-Margarethenhoehe, Germany,

assignor of one-half to Karl Adler, Washington, D. C.

Application October 25, 1950, Serial No. 195,257

Claims priority, application Germany October 28, 1949 4 Claims.

The present invention relates to an arrangement for reducing the recoilof percussive tools such as hammers that are operated by compressed airand especially hammers wherein the lower edge of a multi-stepped tubularvalve is used for opening and closing the exhaust ports through whichthe operating air escapes after the working stroke.

In such hammers the exhaustports extend substantially to the top due tothe fact that the relatively short tubular valve is located near the topof the hammer so that only a small compression chamber is available forthe returning piston. Such a compression chamber, however, is necessaryfor absorbing the kinetic energy of the mass represented by thereturning piston. If the compression chamber is small, the energyexerted by the returning piston must also be of small magnitude. if thelatter were oi great magnitude the compression produced would beexcessive and the recoil would be excessive. Therefore, in order to beable to absorb a large amount of piston recoil energy despite thediiiiculties interposed by the nature of the control valve systemmentioned above, the control means must be disposed at a deeper point inthe cylinder, or, what amounts to the same thing, the compressionchamber must be lengthened. lncreasing the compression chamber howeverreduires the provision of an increased and harmful space, or, whatamounts to the same thing, the non-utilized piston stroke will beincreased in length because the compression pressure must not bepermitted to become excessive.

In order to produce satisfactory hammers despite the presence ofcompression chambers oi short constructional height, the energy of thereturning piston is absorbed, in accordance with the present invention,by causing the returning piston to slide into a cap, hereinafter calleda recoil cap, the piston tting in sealing relation in said recoil capand serving to form a compression chamber therein. The recoil cap isbuffered by the pressure medium so that said cap acts as a resilientbuffer as soon as the pressure rises excessively or when sudden shortpressure surges are produced by the piston in its return travel into thecompression chamber of the recoil cap. On the other hand, the recoil capshould be able to travel back along with the piston in order thus totake up any residual kinetic energy still present in the piston whichcould not be absorbed in the compression chamber of the recoil cap.

Attempts have been made heretofore to absorb the recoil by means of anair dashpot, but the arrangements proposed therefor were not successfulnor were they based on the method underlying the present invention.

This divided absorption of the kinetic energy of the returning piston,effected by the incorporation of a recoil cap, serves to reduce theconstructional length of the entire controlling mechanism to asubstantially greater extent than would be possible if no recoil cap isused, because the greater portion of the energy of the returning pistonis used up in moving the recoil cap, so that the compression stroke ofsaid cap can be reduced. It is obvious that the power absorbing capacityof the recoil cap depends on the size of the surface thereof subjectedto the pressure medium.

The invention oiiers the following advantages: a. The possibility ofabsorbing a large amount of piston recoil energy by means of a shorteffective compression space, thus increasing both the speed of thereturning piston and the number of blows struck by the piston without,hcwever, thereby producing more violent recoils.

b. Insuring full use of the piston stroke, thus attaining the mostpowerful piston blows possible.

c. Achieving the greatest possible economy in air consumption inasmuchas the harmful space needed for compression and disposed ahead of therecoil cap can be kept as small as possible.

d. If the recoil energy of the piston is reduced, that is, due to beingexpended on softer material, smaller or even no recoil movements will berequired of the recoil cap. Consequently the piston stroke will bereduced, the number of blows will increase and the piston blows willbecome weaker, that is, a hammer having an incorporated recoil cap willautomatically increase its stroke and hence its percussive force as thepiston return energy increases, that is, as the rebounds becomestronger, such as are engendered when harder material is operated on.

Tests made in actual practice have demonstrated the correctness andsignificance oi the present invention. Thus, in the case of a hammerhaving a piston diameter1 ci 35 mm. (1% inches) and a piston stroke ci14o mm. (5l/2 inches), the piston was able to slide rapidly into therecoil cap, the latter being set in motion thereby.

The subject matter of the invention will be illustrated by Way of anumber of embodiments.

The invention is shown in the form of several embodiments in Figures lto 8.

In Figs. 1 and 6 no recoil caps are shown in order to facilitatecomparison with hammers that are provided with recoil caps. In Figs. 1to 8, i and 2 represent the tubular valve that closes and opens theexhaust ports 3; the valve is shown in its lower limit position.

In Figs. 2, 3 and 7, li represents the recoil cap of which the area ofthe at surface 5 acted on by the compressed. air is equal to thepressure affected area of the oppositely facing counteracting surface ofthe cap. in Figs. 4, 5 and 8, the recoil cap is indicated by '5, thearea of the surface 8 thereof acted on by the compressed air beinggreater than the area of the opposite counteracting surface of the capsince in this case the annular surface i is relieved of air pressureload. The recoil caps li and 'i are continuously acted on by compressedair, entering through passageways il, but in the compression chambers I2and it, theheight of which is indicated by i6, the reversal of thetubular valves i, 2 is effected at the expense of the kinetic energy ofthe piston lli. rThe compression-induced pressure in the compressionchambers I2 and i3 should not exceed the operating pressure at all or atmost only to ight extent. Such excess occurs however in the of ha -ersnot preided with recoil caps, such as those shown in Figs. 1 and 6 ifthe height i5 of the compression chamber is very low and if a great dealof energy is provided by the returning piston. Compression valuesamounting' to more 15 atmos. atmospheric (214 lbs. per inch) have beenobserved where the actual operating pressure amounted merely to 6 atmos,above J (85 lbs. per sq. inch). This indicates the tud'e of the recoil.

In the case of the hammers shown in Figs. 2, 3, 4, 5, .7 and 8 anyexcess compression in the compression chambers i2 and ifi would nievethe recoil caps l and i along with piston iii upwardly at the expense ofany residual kinetic energy possessed by the returning piston I4.Although the pressure engendered by compression in the recoil cap s3 isthe same as the operating pressure to start with, thecompression*induced pressure in the recoil caps 'i increases inaccordance with the size ratio prevailing between the area of thepressure-loaded surface 8 and the reduced area of the oppositecounteracting surface. Any airengendered blows that vnay occur in thecornpression spaces l2 and it are absorbed by the cushion formed by airentering through the passageways i i. The recoil caps :i and 'l havetherefore been shown incorporated in a number of the figures in order toindicate the nature of structure required for keeping the height i@ ofthe compression chamber as small as possible and to keep the terminalcompressional height as harm less as possible. The latter in the case oian adiabatic compression assumed to taire place in a perfectlycylindrical compression chamber amounts, theoretically, at an operatingpressure of 6 atmos. above atmospheric, to about 25% of the aforesaidheight, and at an operating presn sure of 4 atmos. in excess ofatmospheric, it amounts to about 32% of the heights represented by thenumerals i5 and i5 if it is desired that the compression-engenderedpressure should be equal to the operating pressure of 6 and 4atmospheres above atmospheric (85 lbs. per sq. in. and 5'? lbs. per sq.in.) respectively.

Figs. 1 to 5 show a three-step tubular valve l of usual construction andof the reciprocally actuated type; this serves to open and close theoperating air exhaust ports 3.

Figs. 6, 7 and 8 show tubular valves of the twostep type wherein thefunction of the unloading step Va' of the three-step tubular valve Ishown in Figs. 1 to 5 is performed by the unloading step it (in Figs. 6,7 and 8) by having the recoil cap i extend into the two-step tubularvalve 2 in air-sealed but sliding relation, a guide bushing is thereforbeing shown in Figs. 6 and '7, and the recoil cap 'I serving as acontrol bushing in Fig. ES. The two types of tubular Valves l and 2operate in similar fashion.

The recoil cap shown herein for preventing recoil and for making itpossible to absorb large amounts of the energy of the returning pistonis also applicable to all other types of percussive tools includingthose using control means other than those herein shown.

I claim:

1. In a pneumatic percussive tool having a cyln inder, a piston hammerreciproeabie therein, pressure-actuated reciprocable valve meanscontrolled by the movements of the for controlling the admission ofoperating pressure to the cylinder on opposite sides of hammer, thecombination of a cup-shaped irnperforate recoil cap separate from thevalve slideably mounted at the rearward of the cylinder' for compressionof air between d can and the returning piston hammer, the n nmer beingsealingly tele-scopable within said cap for entrapment of airtherebetween in the bowl of said cap, means defining a closed bufferchamber at the rear of said cap, and passageway means constantlyproviding communication between chamber and the operating pressure tothereby constantly subject the rear of cap to the operating pressure.

2. The structure deiined in claim 1, in which the effective pressurearea of the cap exposed. to the operating pressure is greater than thetive pressure area thereof exposed to the air coinpressed between thepiston and said cap.

3. The structure deiined in claim 1, in which the valve means is ofmulti-stepped tubular form with the piston slideable therein, and therecoil cap is telescopingly and sealingly engageabie with the rearwardend of the tubular valve mea- 4, rlhe structure deiined in claim 1, inwl the valve means is of two-Step tubul r forin the piston slideabletherein, and the c i telescopingly and sealingly engagea'ole within therearward end of the tubular valve means.

FRANZ References Cited in the file of this patent UNITED STATES PATENTSNumber Name Date 727,431 Peck May 5, 1903 996,880 Oldham July 4, 197.1

1,071,263 Robertson Aug. 1913 1,352,191 Henig Sept. '7, 1920 1,460,272Rehfeld June 1923 1,582,614 Kusunoki et al Apr. 2?, 1926 1,739,338Wadsworth "Dec, 10,

